Friday, March 13, 2015

Repairing and Regenerating the Intervertebral Disc

The spine has always been an area of relative mystery for science as a whole, and medical conditions involving the spine are usually perceived as serious. However, the idea of using stem cells has been introduced in the practice of repairing the degenerating intervertebral discs of aging humans. The intervertebral disc is located in the spinal cord and acts as a buffer between different vertebrae and nerves. The degeneration of the disc, which is common in middle-aged people, can lead to a variety of problems including chronic back pain. However the relatively unknown tasks of the cells comprising this structure has lead to difficulties in treating it.
As humans age, the intervertebral disc tends to break down. The essential material, proteoglycan, which provides the hydration to the intervertebral disc, begins to break down and in turn the disc becomes deformed. Additionally collagen, which is abundant in the entire disc, also changes in quantity and in type. Both of these substances begin to break off, and in turn fragment into smaller pieces, taking away essential protein from the disc. Additionally, because of the fragmentation and loss of hydration the disc becomes jumbled in its structure. Without the support of the intervertebral disc, the vertebrae have extra stress, which leads to the back problems that many people encounter.

Nevertheless, stem cells have been introduced as a possible treatment for the degeneration of the intervertebral disc. More specifically, Mesenchymal Stem Cells have been introduced, which can be found in adult bone marrow. These stem cells in particular have been shown to have exceptional repairing ability, for example in heart muscles, which is why they were highlighted over other varieties of stem cells. Scientists have begun experimental treatments on smaller animals like rabbits, in which they inject these stem cells into the intervertebral disc and see if regeneration occurs. Within the intervertebral disc lie two distinct parts, the nucleus pulposus and the annulus fibrosus. The nucleus pulposus is at the center of the intervertebral disc and the annulus fibrosus is at the next layer out. The notochordal cells that lie within the nucleus pulposus are hypothesized to be critical to the composure of the intervertebral disc because they produce the proteoglycan, which creates a protein that comprises the intervertebral disc. However, for an unknown reason these cells are diminished throughout a human’s lifespan, hence the stem cells efforts.

https://ittcs.files.wordpress.com/2010/05/img_0181.jpg

Scientists have made ground in finding the most efficient process to inject these cells and have them perform to the maximum potential. In a trial on rabbits, scientists injected autogenic stem cells into the rabbits and monitored the change in the intervertebral disc, specifically whether it would regenerate or not. In a four-week period the disc did not regenerate but the degeneration was in fact halted, which is a promising sign for the future prospects of the technique.

There were also alternative trials to this, in which the scientists injected allogenic cells, cells from another individual, into the intervertebral disc and noted the results. The use of allogenic cells bypassed several difficulties that cells from the own individual faced. These stem cells were of ample supply to begin with, so there would be no real limitation if this trial were to be . Furthermore, scientists believe that genetic predisposition might be a factor in the degradation of the disc, and without an individual’s own genes in the cells, this problem is avoided. Lastly, the worry of immunogenicity is avoided in this scenario, because these cells aren’t recognized as an invader to the individual’s immune system and are allowed to operate. This trial was extended out over a six month time period, with rabbits again, and the results were even more promising. The stem cells produced the proteoglycan and the collagen needed to regenerate the disc without the added difficulties of autogenic cells.

Scaffolds are also used to help integrate stem cells into the disc. The importance of injecting these stem cells surrounded by what they naturally would be in the body was highlighted in another test performed. These nucleus pulposus cells were injected into the intervertebral disc. However some were injected into the disc in their natural state, surrounded by liquid plasma, and some were injected on their own. The results found showed that the cells injected in a state closer to their natural habitat were much more successful in regenerating the intervertebral disc.

While all of these tests point to a potential for an incredible treatment, many questions still linger. Gene therapy is an advanced science that society has yet to fully grasp. Along with this, the intervertebral disc and how it operates. Namely, scientists need to figure out which genes operate in the intervertebral disc, and how they cause the degeneration in humans. Thus far only small animal trials have taken place, and these animals are different genetically than humans. Therefore there is much that needs to be learned about the process, about its feasibility, and about its usefulness.

3 comments:

As someone who herniated a disc in my lumbar spine several years ago, I think it's amazing that scientists are looking into the use of stem cells to help repair degenerative discs rather than high-risk surgeries like khyphoplasty. However, a large majority of the pain that people with disc problems experience is due to the disc being dislodged or deformed in such a way that it pushes on the nerves in the spinal column, so I would be interested to see whether these treatments can retain the structural integrity of the disc so that they do not press on the nerves.

For a long time I've been interested in the potential of using stem cells for regenerating neural tissue. It's certainly a challenge, and I'm glad to see that there's been a lot of progress. It's particularly interesting to me that stem cells from other people work better, and also are not seen as invading cells. Although gene therapy shows immense promise in treating a wide variety of conditions, it seems that the stem cell therapy will probably be available before then. Hopefully the results of this experiment will help researchers and doctors figure out how to repair damages in other neural tissues.

I found this post especially interesting because after years of gymnastics I developed spondylolysis, which is a stress fracture in the fifth lumbar vertebra. My fracture never healed properly because a fibrous capsule surrounded the fracture and didn't allow it to heal properly. As a result, extra stress was put on the disk directly below the vertebra and has since been degenerated. This old injury causes me pain to this day. The idea of regenerating disks using stem cells would improve sports medicine greatly because my injury is actually a fairly common one among athletes. I feel like this innovation would cut recovery time in half, maybe even less (it took me 5 years to "recover," and I'm still not 100% recovered).